Recovery of heat from the combustion products of a gas turbine engine

Abstract: Heat is recovered from the combustion products of a gas turbine engine, bypassing an endothermic fuel through a heat exchanger (50) arranged in the exhaust section (44) of the gas turbine engine prior to burning the fuel in the combustion section of the engine. In one embodiment, the fuel is decomposed by a catalyst provided in a fuel flow path (66) of a second heat exchanger (64) heat being provided to said second heat exchanger by air bled from the compressor (22) of the engine. In another embodiment, fuel is decomposed in the heat exchanger (50) itself.

Description: This invention relates to a method for managing the energy produced by a gas turbine engine. One of the considerations in selection of gas turbine engine for a particular application is the overall thermodynamic efficiency of the engine. For aircraft operators such as commercial airlines, thermodynamic efficiency is critical to operating the airline at a profit. Military operators of aircraft are likewise concerned about thermodynamic efficiency, since thermodynamic efficiency determines the effective range of a particular aircraft. The thermodynamic efficiency of industrial gas turbines, such as those used to generate electricity, directly affects the cost of operation thereof. Lower thermodynamic efficiency results in higher costs to the consumer, and/or lower profits to the electric power industry. Therefore, there is an ongoing pursuit to increase the thermodynamic efficiency of gas turbine engines. What is needed is a method of providing efficient energy management of a gas turbine engine to yield a significant increase in the overall thermodynamic efficiency thereof. It is therefore an object of the present invention to provide a method for increasing the overall thermodynamic efficiency of a gas turbine engine. US-A-3018626 discloses a method of recovering thermal energy from combustion products of a gas turbine engine having the features of the preamble of claim 1 and a gas turbine engine having the features of the preamble of claim 3. US-A-5161365 discloses an endothermic fuel power generator. From a first aspect, the invention provides a method of recovering thermal energy from combustion products of a gas turbine engine, said engine having in serial flow arrangement a compressor section for compressing ambient air to produce compressed air, a combustion section for mixing fuel with said compressed air and igniting said fuel and compressed air to produce said combustion products, a turbine section for expanding said combustion products and driving the compressor section, an exhaust section for conveying said combustion products from said turbine section and out of said gas turbine engine; said method comprising providing a first heat exchanger located in said exhaust section and exposed to said combustion products, said heat exchanger having first and second flow paths extending therethrough, each flow path having an inlet and an outlet; and flowing said combustion products through the first flow path of said first heat exchanger; characterised by further providing a combustible endothermic fuel source; pumping fuel from said source to the combustion section of said engine through the second flow path of said first heat exchanger, thereby heating said fuel while simultaneously cooling said combustion products, said second flow path including a catalyst that decomposes the endothermic fuel into gaseous fuel; and providing an auxiliary turbine, said auxiliary turbine having an auxiliary shaft for providing power to mechanical accessories, and delivering gaseous fuel exiting said heat exchanger to said auxiliary turbine and expanding said gaseous fuel through said auxiliary turbine, thereby providing work to drive the shaft. From a second aspect, the invention provides a gas turbine engine having in serial flow arrangement a compressor section for compressing ambient air to produce compressed air, a combustion section for mixing fuel with said compressed air and igniting said fuel and compressed air to produce said combustion products, a turbine section for expanding said combustion products and driving the compressor section, an exhaust section for conveying said combustion products from said turbine section and out of said gas turbine engine; a heat exchanger located in said exhaust section and exposed to said combustion products, said heat exchanger having a first flow path for said combustion products and a second flow path extending therethrough, each flow path having an inlet and an outlet; characterised in that it further comprises a combustible endothermic fuel source; means to pump fuel from said source to the combustion section of said engine through the second flow path of said first heat exchanger, to heat said fuel while simultaneously cooling said combustion products, said second flow path including a catalyst that decomposes the endothermic fuel into gaseous fuel; an auxiliary turbine, said auxiliary turbine having an auxiliary shaft for providing power to mechanical accessories; and means for delivering gaseous fuel exiting said heat exchanger to said auxiliary turbine and means for expanding said gaseous fuel through said auxiliary turbine, thereby providing work to drive the shaft. An endothermic fuel recovers heat energy from the combustion products of a gas turbine engine downstream of the turbine, and returns that energy to the combustion section of the engine upstream of the turbine. The heat energy of the combustion products downstream of the turbine is used as the heat source to decompose the endothermic fuel into high pressure gases in the presence of a catalyst. The method of preferred embodiments results in a reduction in net specific fuel consumption and a reduction in exhaust temperature, which in turn yields reduced levels of fuel consumption and exhaust product emissions. A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawing, which illustrates schematically the invention applied to a turboshaft gas turbine engine. The preferred embodiment shown provides a method for utilizing the large heat sink capacity of endothermic hydrocarbon fuels to manage the energy flow in gas turbine engines in a manner providing improved thermodynamic efficiency thereof. The method involves managing the energy produced by a gas turbine engine, and is applicable to vehicles such as aircraft which are powered by turbojet, turbofan and turboshaft engines, as well as stationary applications thereof. In the preferred embodiment of the present invention, the method is shown and described in terms of a turboshaft engine 150 which uses an endothermic fuel source 14 that supplies the fuel to the engine 150 via a fuel pump 16. The engine 150 includes, in serial flow arrangement, a compressor section 152 for compressing ambient air, having a single compressor 154 to produce compressed air 26. Aft of the compressor section 152 is a combustor section 28 for mixing fuel with the compressed air 26 and igniting the fuel and compressed air 26 to produce combustion products 30. Aft of the combustion section 28 is a turbine section 156 for expanding the combustion products 30 and driving the compressor 154 of the compressor section 152. The endothermic fuel source 14 is essentially at ambient conditions, while the combustion products 30 are at a substantially higher temperature. The turbine section 156 has a single turbine 158. The turbine 158 drives the compressor 154 via the engine shaft 160 which connects the turbine 158 to the compressor 154. Additionally, a gear box 162 having an output shaft 164 is connected to the engine shaft 160, for increasing or decreasing the rotational velocity of the output shaft 164 relative to the rotational velocity of the engine shaft 160. Aft 42 of the turbine section 156 is an exhaust section 44 for conveying the combustion products 30 from the turbine section 156 out of the gas turbine engine 150. The exhaust section 44 of the turboshaft 150 utilizes a recuperative heat exchanger/reactor 166 located adjacent to, or incorporated into, the engine case. The recuperative heat exchanger/reactor 166 has first 52 and second 54 flow paths extending therethrough, and each flow path has an inlet 56, 58 and an outlet 60, 62. The first flow path 52 of the recuperative heat exchanger/reactor 166 is exposed to the combustion products 30, and the combustion products 30 flow through the first flow path 52 thereof. The second flow path 54 of the recuperative heat exchanger/reactor 166 has a catalyst, specifically selected based on the desired endothermic fuel, coated or packed therein in a manner such that the fuel flowing through the second flow path 54 of the recuperative heat exchanger/reactor 166 is in intimate contact with the catalyst. An auxiliary turbine 168 having an inlet 170 and an outlet 172 is likewise provided, and the auxiliary turbine 168 is connected to a power take-off shaft 174 to provide mechanical energy to power accessories as desired. A first conduit 176 is connected at one end to the fuel pump outlet 178 and at the other end to the inlet 58 of the second flow path of the recuperative heat exchanger/reactor 166. The outlet 62 of the second flow path 54 of the recuperative heat exchanger/reactor 166 is connected by a second conduit 180 to the inlet 170 of the auxiliary turbine 168 to deliver the fuel exiting the second flow path 54 of the recuperative heat exchanger/reactor 166 thereto. The outlet 172 of the auxiliary turbine 168 is connected to a third conduit 182 which routes the gaseous fuel to the combustion section 28 of the turboshaft 150. In operation, the combustion products 30 flowing from the turbine section 156 flow into the inlet 56 of the first flow path of the recuperative heat exchanger/reactor 166 and flow through the first flow path 52 thereof. Endothermic fuel from the fuel source 14 is pumped by the fuel pump 16 through the first conduit 176, is delivered to the inlet 58 of the second flow path of the recuperative heat exchanger/reactor 166, and flows through the second flow path 54 thereof. Within the recuperative heat exchanger/reactor 166, the combustion products 30 are cooled simultaneously with the heating, decomposition, and gasification of the fuel in the second flow path 54 through the transfer of heat energy from the combustion products 30 to the fuel. The combustion products 30 then exit the first flow path 52 of the recuperative heat exchanger/reactor 166 through the outlet 60 thereof, and the gaseous fuel exits the second flow path 54 of the recuperative heat exchanger/reactor 166 through the outlet 62 thereof. The gaseous fuel exiting the recuperative heat exchanger/reactor 166 is delivered to the inlet 170 of the auxiliary turbine 168 through the second conduit 180 and expanded through the auxiliary turbine 168. The power extracted by the auxiliary turbine 168 via the power take-off shaft 174 can be used to satisfy mechanical power or accessory requirements, instead of using mechanical power extraction from the engine 150. The gaseous fuel exiting the outlet 172 of the auxiliary turbine is delivered through the third conduit 182 to combustion section 28 where it is mixed with compressed air 26 exiting the compressor 154, ignited, and combusted. By pumping the endothermic fuel to high pressure prior to delivering the fuel to the recuperative heat exchanger/reactor 166 to absorb energy from the combustion products 30 in the exhaust section 44, the gaseous fuel provides an excellent working fluid for expansion in the auxiliary power turbine 168. The heated reaction products are composed of mixtures of hydrogen and light hydrocarbon gases, and provide a potential for a large source of mechanical power. The regenerative recovery of energy from the combustion products 30 in the exhaust section 44 of turboshaft engines, and stationary power plants as well, provides a means of improving the overall cycle efficiency. Although the foregoing embodiment of this invention has been shown and described with respect to a turboshaft, the embodiment can be used on a turbofan or turbojet as well, since the method is not dependent on the differences between turbofan, turboshaft, and turbojet engines.

Claims: A method of recovering thermal energy from combustion products (30) of a gas turbine engine, said engine having in serial flow arrangement a compressor section (18;152) for compressing ambient air to produce compressed air, a combustion section (28) for mixing fuel with said compressed air and igniting said fuel and compressed air to produce said combustion products, a turbine section (32;156) for expanding said combustion products and driving the compressor section, an exhaust section (44) for conveying said combustion products from said turbine section and out of said gas turbine engine; said method comprising providing a first heat exchanger (50;166) located in said exhaust section and exposed to said combustion products, said heat exchanger having first (52) and second (54) flow paths extending therethrough, each flow path having an inlet (56,58) and an outlet (60,62); and flowing said combustion products (30) through the first flow path (52) of said first heat exchanger (50; 166); characterised by further providing a combustible endothermic fuel source (14); pumping fuel from said source (14) to the combustion section (28) of said engine through the second flow path (54) of said first heat exchanger, thereby heating said fuel while simultaneously cooling said combustion products, said second flow path (54) including a catalyst that decomposes the endothermic fuel into gaseous fuel; and providing an auxiliary turbine (168), said auxiliary turbine having an auxiliary shaft (174) for providing power to mechanical accessories; and delivering gaseous fuel exiting said heat exchanger to said auxiliary turbine (168) and expanding said gaseous fuel through said auxiliary turbine, thereby providing work to drive the shaft (174). The method of claim 1 wherein the method is used in a turboshaft engine, said compressor section including a compressor (154) attached to a shaft (160) said turbine section including a turbine (158) attached to said shaft, and a gear box (162) being connected to said shaft. A gas turbine engine having in serial flow arrangement a compressor section (18;152) for compressing ambient air to produce compressed air, a combustion section (28) for mixing fuel with said compressed air and igniting said fuel and compressed air to produce said combustion products, a turbine section (32;156) for expanding said combustion products and driving the compressor section, an exhaust section (44) for conveying said combustion products from said turbine section and out of said gas turbine engine; a heat exchanger (50;166) located in said exhaust section and exposed to said combustion products, said heat exchanger having a first flow path (52) for said combustion products (30) and a second flow path (54) extending therethrough, each flow path having an inlet (56,58) and an outlet (60,62); characterised in that it further comprises a combustible endothermic fuel source (14); means to pump fuel from said source (14) to the combustion section (28) of said engine through the second flow path (54) of said first heat exchanger, to heat said fuel while simultaneously cooling said combustion products, said second flow path (54) including a catalyst that decomposes the endothermic fuel into gaseous fuel; an auxiliary turbine (168), said auxiliary turbine having an auxiliary shaft (174) for providing power to mechanical accessories; and means for delivering gaseous fuel exiting said heat exchanger to said auxiliary turbine (168) and means for expanding said gaseous fuel through said auxiliary turbine, thereby providing work to drive the shaft (174).

Inventors: COONS LELAND L, GLICKSTEIN MARVIN R, COONS, LELAND L, GLICKSTEIN, MARVIN R
Applicants: UNITED TECHNOLOGIES CORP, UNITED TECHNOLOGIES CORPORATION
Application year: 1994
Main classification: F02C7
IPC codes: F02C6, F02G5, F02C7